1. Field of the Invention
This invention relates generally to demodulation systems, and, more specifically, to GFSK or GMSK demodulation systems configurable in response to channel conditions.
2. Related Art
Current GFSK (Gauisian Frequency Shift Keying) or GMSK (Gauisian Minimum Shift Keying) demodulators are collectively used widely in various wireless communications systems including, for example, Bluetooth, Wireless LAN, Home RF, DECT, and GSM cellular systems. Since GMSK demodulators are a subset of GFSK demodulators, for purposes of this disclosure, these two will be referred to collectively as GFSK demodulators.
In these applications, such demodulators are subject to diverse forms of interference, including, without limitation, Adjacent Channel Interference (ACI), Co-Channel Interference (CCI), and Inter-Symbol Interference (ISI). Unfortunately, conventional demodulators are not adept at simultaneously rejecting all forms of interference.
Various additions have been made to differential demodulators in an attempt to deal with this problem, including Decision Feedback Equalizers (DFE) and Maximum Likelihood Sequential Estimators (MLSE) receivers. However, such additions tend to be complex and expensive, and therefore unsuitable for mass market devices.
The invention provides a GFSK demodulation system where a baseband signal is input into a plurality of detectors. At least one of the detectors may be configured to better handle a particular form of interference than one or more of the other detectors. For example, one of the detectors may be a differential phase detector adept at rejecting ACI, while another may be an FM detector adept at rejecting CCI. In another example, two of the detectors may be differential phase detectors configured to determine phase differences over different time periods. The time periods may be selected so that at least one of the detectors is better able to handle a form of interference than the other detector.
The outputs of the detectors may be soft estimates which are input in parallel to corresponding signal quality estimators and the parallel data inputs of a multiplexor. Each signal quality estimator may provide a performance metric for the output of the corresponding detector. Each performance metric provides a measure of the quality of the corresponding output from the detector. The performance metrics are provided to the selector over one or more signal lines. Responsive to the one or more performance metrics, the selector selects, or continues the pre-selection of, one of the detectors. A multiplexor then outputs the estimated bits from the selected or pre-selected detector. The output of the multiplexor may be input to a decision module. The decision module may compare the output of the multiplexor with a threshold, and based on this comparison, provide hard estimates of the source bits.
One of the detectors may be pre-selected, such that the output of this detector at least initially appears at the output of the multiplexor. During a prescribed time period, the signal quality estimators may provide to the selector performance metrics for each of these detectors. Responsive to these performance metrics, the selector may then select another detector for output at the multiplexor. Alternatively, the selector may simply continue the preselection of the default detector.
Alternately, none of the detectors may be preselected. During a prescribed time period, the signal quality estimators may provide to the selector performance metrics for one or more of the detectors. Responsive to these performance metrics, the selector may then select one of the detectors for output at the multiplexor.
The invention also provides a second embodiment of a GFSK demodulation system where a signal is input to a detector which has a plurality of possible operating modes, and which is configurable to operate in accordance with a particular mode selected or pre-selected by the selector. At least one of the possible modes may be better able than one or more of the other modes to handle a particular form of interference.
For example, the detector may be a differential phase detector where the delay between successive phase samples (hereinafter, the xe2x80x9csampling delayxe2x80x9d) used to compute xcex94xcex8 is configurable responsive to the mode which is selected or pre-selected by the selector. The detector may initially utilize a default sampling delay. However, after a prescribed time period, the selector may select a different sampling delay.
The invention also provides a third embodiment of a GFSK demodulation system which is a combination of the foregoing two embodiments. In particular, a signal may be input to first and second detectors. One of the detectors is selected or pre-selected for output at the multiplexor. In addition, the selected detector has a plurality of possible operating modes, one of which is selected or pre-selected. The detector is then configured to operate in accordance with the selected or pre-selected mode of operation.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.